Telephone system



Oct. 26, 1943.

G.- HECHT ET AL TELEPHONE SYSTEM Filed May 1, 1942 STA T/OA! 5 sheets-sheet 1 SEA/DER SELECTOR FIG- .5

FIG. 2 FIG-8 G. HECHT INVENTORS A. A. L U/VDSTROM ER. TAYLOR Bra 6 Mi A TTORNEV Oct. 26, 1943. HECHT ETAL 2,332,912

TELEPHONE SYSTEM Filed May 1, 1942 5 Sheets-Sheet 2 a. HECHT lNl/EN 7:0RS: A. A. LUNDSTROH ER. TAYLOR ATTORNEY Oct. 26, 1943. G. HE'CHT ETAL TELEPHONE SYSTEM 5 sheets-sheet 5 Filed May 1, 1942 G. HECHT INVENTORS A. A. LU/VDSTROM E. R. TAYLOR BV A TTORNEV Oct. 26, 1943. HECHT ET AL TELEPHONE SYSTEM Filed May 1, 1942 5 Sheets-Sheet 4 SR T T T HNW. .A CUA 216 MR GAE? T- Ff K Patented Oct. 26, 194-3 UNITED STATES PATENT TELEPHQNE SYSTEM George Hecht, Astoria, N. Y., Alexis A. Lundstrom,

East Orange, N. .l'., and Edmund R. Taylor, Pelham Manor, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 1, 1942, Serial No. 4141,3319

23 Claims.

composed of a combination of frequencies lying within a comparatively narrow signaling band.

Another object of the invention is a novel arrangement in the receiving circuit for checking the accuracy of the frequency combinations of the signal impulses as the same cause the receiver to respond to the frequencies of which the pulses are composed.

Still another object of the invention is the provision of means for protecting the receiving circuit of the signaling system against false registration of current frequencies not present in a pulse, current frequencies which, for example, might be produced bynoise, speech and the like, and this object is attained. by a novel circuit arranged to respond to a relatively long pulse which is transmitted ahead of the regular signal impulses and composed of a suitable combination of the signal frequencies themselves. The proper response of this circuit to the relatively long pulse, initiates the operation of other parts of the receiver by which the latter is caused to be placed in a condition to effectively register the signal impulses that follow.

Still another object of the invention is the provision of a circuit arrangement in the receiver whereby, in the event of prolonged signal impulses, duplicate registration is prevented.

Still another object of the invention is the provision of a suitable check circuit in the receiver which, in response to the received signal impulses, operates to indicate Whether each of the impulses contains the exact number of frequencies required or whether it contains more than such frequencies, in the former case causing the receiver to register the received impulse and in the latter case to cause the reeeiver to block such registration.

Theseand other objects of the invention will be more readily ascertained from the following description and appended claims, taken in con nection with the following drawings in which: Fig. 1 shows the transmitting station, a trunk line to which such station may be connected, selecting apparatus by means of which the receiving circuit of the invention may be connected to the trunk and to the transmitting sta tion; and a skeletonized showing of two te1ephonic connections which may be established by settable apparatus responsive to the operation of the receiver;

Fig. 2 shows the amplifier and detector circuit of the receiver;

Fig. 3 shows the check circuit for checking the accuracy of the received impulses and the circuit which. responds to the conditioning or KP impulse;

Fig. i shows a group of conventional registers settable in response to the received impulses, and a conventional showing of a circuit known as a marker which is adapted to operate in response to the setting of some of the registers to aid in the selective positionin of switching apparatus by which parts of the telephone connections shown in Fig. 1 may be set up;

Fig. 5 shows an alternative arrangement of settable registers; while Fig. 6 shows the manner in which Figs. 1 to 5, inclusive are to be disposed relative to each other in order to disclose the invention completely.

It will be readily understood by those skilled in the signaling arts that a signaling system a1'- ranged for transmitting and receiving alternating current impulses is adaptable to a wide variety of uses, especially indicated by the application to be made of the intelligence conveyed by the impulses transmitted over the system. Uur invention may, of course, be utilized for any purpose indicated by the use which is to be made of the impulses, and in order to describe the elements of the invention, its operation and its flexibility, we have chosen to disclose it in conction with its adaptation to a telephone sysof the kind described in Patent 2,288,251, issued to P, B. Murphy on June 30, 1942, in which a calling subscriber, desiring a connection with a distant station which can only be reached by trunking facilitites available at an operators position in an office within the dialing area of the calling subscriber, dials the operator who, upon receiving from the calling subscriber the office and line number of the desired station, selects a trunk extending in the desired directionand causes a group of alternating current impulses indicative of the called oiiice and station designations to be transmitted thereover into settable apparatus at the oiiice in which the trunk terminates, whereirom this apparatus then controls the selective positioning of a suitable number of switches by means of which the trunk connection is further extended to the desired station. It is obvious, however, that while this application of the invention will illustrate its scope and operation, the invention itself is susceptible to other uses readily appreciated by those skilled in the signaling art.

Referring, now, to the drawings, the subscriber A establishes a connection to the operators position within his dialing area by the Well-known means referred to in said patent, and, at said position, herein referred to as the transmitting station, informs the operator thereat that he desires to establish a connection to subscriber B whose station terminates in office Y, which can be reached from the transmitting station over a trunk line that interconnects said transmitting station with ofdce X and by automatic trunking facilities between oifice X and office Y which are selectively connectable to the trunk therebetween by equipment at ofiice X, which operates in response to the receiving circuit of our invention as the same responds to the impulses transmitted over the trunk from the transmitting station. The operator, upon learning of the desired omce and station from the calling station A, selects an available trunk, say the trunk which terminates in jack JA having the conductors T and R ex tending to the ofiice X, and, by suitable equipment disclosed in said patent causes conductors SCT, and SCR, of the key-set KS at her position to become connected through the right-hand plug of the cord and jack JA to conductors T and R, respectively, of the trunk thus taken into use.

The key-set KS at the operators position comprises a series of digit keys -9, a key ST and a key KP, and all of these keys are suitably wired to six separate sources of alternating current frequencies a 7'' within the voice frequency range, in a manner such that the depression of each of the keys will cause two of the frequencies to be applied across conductors T and R of the trunk via conductors SCT and SCR' in the following combinations through circuits completed from the sources of frequencies involved and the undesignated resistances connected to the stationary springs of the keys:

Key 1 Frequencies At office X, the trunk selected by the operator automatically causes the connection thereto of an idle register sender over suitable selecting equipment, for example, a sender selector device SS comprising a crossbar switch and circuits for the control thereof. Into this register sender is incorporated the receiving circuit of our invention; that is, the circuit which receives the alternating current impulses that will be transmitted by the operator by the manipulation of the keyset KS, and this receiving circuit, upon receiving the impulses, first checks them for accuracy and then causes them to become set up on groups of settable registers connected to the receiver. From the registers, the registration therein is then transferred to a marker circuit, and the marker, in response to the transferred registration, then controls the operation of a crossbar trunk selector TS by which the trunk T, R, between the transmitting station and ofiice X is selectively positioned into connection with another trunk that extends between office X and ofiice Y, at which latter office the sender at office X then controls the selective positioning of various other selectors by which the connection is further extended to the terminals of the called line.

In view of the fact that the sender and marker are well-known equipment elements now extensively utilized in automatic telephony, the same being disclosed-and amply described in the above- .mentioned patent and other patents therein referred to, and since the present invention is confined to a signaling system the receiving portion of whichis incorporated in such a sender only by way of disclosing the parts, principles and operation of the receiving circuit, neither the sender nor the marker is disclosed except by conventional indication, the disclosure of the sender being confined to the incorporated signal-receiving circuit in its entirety and to a schematic showing of typical settable registers operating in response thereto.

The receiving circuit of our signaling system, shown in Figs, 2 and 3, is essentially a circuit for translating alternating current signal impulses consisting of various combinations of frequencies sent out from the transmitting station two at a time, into direct current indications suitable for registration in an associated settable register which, comprising a part of the sender, operates in response to'the registration to complete the call in the usual manner.

The receiver of our signal system comprises a volume limiter VL; a signal present channel including the transformer SPT, a vacuum tube S, a polarized relay SPR and associated circuit; a plurality of receiving charmels, one for each frequency in the entire signal band a 1, each of which comprises a band-pass filter BPF, a vacuum tube T and a polarized relay R such as, for instance, the channel reserved for frequency a which is made up of band-pass filter BPFa, a vacuum tube Ta, and a relay Ra; the key-pulse signal circuit comprising relays KP! KP3 and associated circuits which operate in response to the initial operation of relays Re and Rf of the channels reserved for frequencies 0 and 1, respectively, when the key KP is operated at the transmitting station as hereinafter set forth; and the check circuit comprising relays CK! CKS'and associated networks which operate in the manner hereinafter set forth to check the pulses as they are received by the various channels affected by the frequencies in the impulses.

The alternating current signals, which are alternating current voltages across conductors T and R of the trunk, are received and applied to the input elements of the receiving circuit after relay SW is operated in any suitable manner. The input elements of the receiving circuit comprise the adjustable pad AP, which is a means for adjusting the sensitivity of the receiving circuit to the minimum required since, by keeping the sensitivity as low as possible, the likelihood of false operation on currents which may be produced by speech or noise i materially reduced; the high-pass filter designated HPF, the terminating resistance IN the center tap of which is grounded; and the input transformer IT the input winding of which is connected to the terminals of resistance IN and the output winding of which is connected to the common terminal of resistance RGI and paralleled condenser CGI, and the common terminal of resistance RG2 and paralleled condenser 0G2. The other comm-on terminal of resistance RG! and condenser CGi is, in turn, connected to grid Gl of vacuum tube Ll while that of resistance RG2 and condenser 0G2 is connected to grid G2 of vacuum tubes L2. High-pass filter HP? at the receiver input is employed to suppress the unwanted frequencies below the signaling frequency band which may be present in the signal. Since the currents produced by contact and line noise increase in intensity as they decrease in frequency, the probability of false operations from this source is reduced.

The volume limiter VL comprises the pentode vacuum tubes LI and L2 and their associated input'and output circuits. The tubes are operated in the well-known push-pull relation with the output of their respective anodes connected together by means of retardation coil L and delivered, through the blocking condenser BC and A resistance Ni, to resistance N5. The volume limiter provides adequate amplification of the incoming alternating current impulses to cause operation of the desired channels but, however, limits its output signal voltage to such a value that channels other than those intended to be responsive to the frequencies in the signal will not operate on the transient currents generated at channel filter outputs of filters BPFa EPFr by said signals when they start and stop.

The limiting action of the volume limiter VL is obtained by means of the control grid resistances and condensers RGI, CGI, and RG2, cs2 connected, respectively to the grids of the tubes Li and L2, which resistances and condensers cause the grid bias to become more negative when the alternating signal voltage on the grids becomes high enough to cause them to draw current during the positive half waves. When this condition is reached, the power output of the lim- 3 iter becomes approximately constant regardless of further increases in the grid voltage. The actual point at which limiting occurs is controlled by the bias voltage on the screen grids so! and sec, by the bias Voltage on the control grids G! and G2 and by the inherent limitation on maximum plate current with zero control grid potential and particular screen grid and plate potentials. The desired value of bias potential for the screen grids is obtained from the potentiometer consisting of resistances Pi and P2. The grids G! and G2 are held negative in the normal condition by the voltage drop across the cathode resistance L3.

The output of the limiter VL is divided into two (.5

parts by the resistances N i and N55. The voltage across the resistance N! is applied to the signal present circuit which, as before stated, cornprises the input transformer SPT, vacuum tube S and polarized relay SPR. This circuit responds to the small voltage developed across resistance N! in consequence of any signal transmitted from the transmitting station, which signal, being stepped up by the input transformer SPT, is applied to the grid of the pentode vacuum tube 5,

N3 and IN to the inputs of filters BPFa BPFr which act to separate the signaling frequencies into the bands corresponding to the mid-band frequencies a, b, c, o3, e and 1, respectively.

The resistance network N2, N3 and N4 serves a three-fold purpose: (1) it providesattenuation to afford the desired relationship between channel sensitivity and the output of the volume limiter VL; (2) it affords a relatively constant impedance termination between the filters and the widely varying output impedance of the volume limiter; and (3) it attenuates transient disturbances reflected back from the filters to such an extent that they do not cause objectionable chattor of relay SPR.

The control grid of the tube S is normally held positive by the voltage obtained from the potentiometer made up of resistances P 5 and P5. This positive bias, together with the reduced screen grid voltage obtained by the use of resistance SPRi connected to the screen grid of tube S, improves the operation of the circuit and reduces the effect of tube variations. Condenser SP2 is provided to by-pasS the alternating current around resistance SPRI. Relay SPR has its secondary (S) ,or bias,winding connected in the plate circuit of the tube S, while its primary winding (P), or operate, winding is connected to battery through the low resistance filtering retard coil FLT. When there is no signal present on the trunk and, therefore, no signal voltage is being applied to the grid of the vacuum tube S, the plate current flowing through the bias winding of the relay SPR is sufiiciently large to overcome the effect of the current in the operate winding and the relay remains normal; that is, with its armature resting on its lower or unwired contact. But when an alternating current signal is applied to the grid of the tube, the plate current is reduced due to the change in the potential of the grid, and the current through the operate winding (P) of the relay SPR overcomes the reduced current through the secondary Winding (S) and the relay is caused to operate and move its armature into engagement with its upper contact.

The plate circuit of the tube S includes retardation coil SP! and condenser SPCN. These serve two purposes; first, to reduce modulation products that would cause the relay SPR to chatter and, second, to slow up the operate and release times of relay SPR by delaying the dying down and building up of the plate current through the secondary Winding of said relay. These delays compensate somewhat for the fact that there is no band-pass filter in the signal present channel, as compared, for example, with filters BPFa BPFr in the signal channels, and aid in preventing the operation of saidsignal channels by transients since as subsequently set forth, without the operation of relay SPR, signal channel relay. operation cannot take place.

' Referring now to the register of Fig. l, and X wiring in the portion of the receiving circuit shown in Fig. 3, the armatures of relays and (3K2 are Inultipled together and ob tain ground via the back contacts of relay CKI, The front contacts of relays SPR and 0K2 are also multiplecl and connected to conductor J, which extends to the armature of the polarized relay TO. From this relay, this conductor is extended via the armature and upper contact of said relay and theNo. 1 contacts of relay CI, which is assumed to be operated in a manner which will be described hereinafter, to conductor L, and thence to conductor Ll andthence to the operate (P) windings of relays Ra Rf; Hence when relay SPR operates in response to a signal forthcoming over the trunk, it applies ground serially over conductors J and LI to the operate windings (P) of all of the channel relays Ra R1, preparing the same for operation when their associated channels will have responded to the frequencies inthe signal as hereinafter set forth. It may be noted that when relay CK2 operates, as described later, it has the same effect as relay SPR, and also that when relay CKI operates, it removes a short circuit from resistance CH2 and thus inserts this resistance in the ground being supplied to the armatures of relays SPR and K2, the purpose of which will be explained later.

When the register of Fig. 5 is used, however, and Y wiring is provided in Fig. 3, the armatures of relays SPR and 0K2 are grounded and their upper contacts are multipled together and connected to conductor J which is extended to the bottom contact of polarized relay PT and to the No. Zarmature of relay TG. From the former relay, this conductor is extended via the armature of said relay to conductor L, which is connected to resistance CH2 and to the armature of polarized relay CKI. It will be noted, however, that the operate windings (P) of the channel relays Ra R are connected to conductor Ll, which is connected to the other end of resistance CH2 and to the lower contact of relay CKI, so that it joins conductor L either directly through the armature and back contact of relay CK! when said relay is released, or via resistance CH2 when said relay is operated. Hence when relay SPR operates in response to a signal forthcoming over the trunk, or when relay CKZ operates, as hereinafter described, ground is applied serially over conductors J, L and L! to the operate windings (P) of all the channel relay Ra Ry, preparing the same for operation when their associated channels will have responded to the frequencies in the signal as hereinafter set forth.

Since the signal presen circuit is connected to the volume limiter VL ahead of the channel filters BPFa BPF: (by virtue of its: connection across the terminals of resistance Ni relay SPR will be operated when any signal of sufficient magnitude is available at the output of the limiter, whereas the channel relays Ra Rf will be operated only when frequencies passable through their correlated channel filters are present in the signal. Now in any signaling system where speed of transmission is essential to insure the maximum utilization of a minimum quantity of apparatus and the signals are transmitted under manual control of a kind that the signals and the time interval between the signals may not be of uniform duration, it is necessary to register a received signal as quickly as possible upon appropriate settable register relays connected to the contacts of the channel relays, to prepare the channelsv for reception of the next signal by releasing the operated channel relays immediately the registration is completed, to connect the contacts of the channel relays to the next settable register even though the: signal is still present, and yet prevent a duplicate registration of the original signal on this next settable register. The signal present circuit, in connection with acircuit controlled by the settable registers as hereinafter set forth, insures the correct performance of these functions by providing means that will cause the operate circuits of the channel relays to remain open once they are opened, even though the signal is still present, and will cause them to remain open untilthe signal is over.

In order to understand how these and other functions are performed, the description of the remaining elements of the receiver will be given in connection with their operation,

When a sender is seized via the sender-selector apparatus SS and connected to the trunk taken into use by the operator at the transmitting station, conductors T and R of the trunk are connected to the signalin conductors T and R and thence via the sender-selector to leads TI and RI, respectively, of the receiver circuit incorporated in the sender, and operations are then initiated in the sender whereby positively grounded battery is connected to conductors BATI and BATZ, it being understood that suitable sources of current (not shown) have already been or are continuously connected to the filaments of all the electronic tubes of the receiver. Battery on conduct-or BAT! completes an obvious circuit through the secondary (S), or bias, windings of polarized relays CKI, CK2 and CK? thereby causing the energization of these windings but not the operation of their respective relays, the normal condition of each of which may be assumed to be with the armature engaged with the lower contact as shown. Batter over conductor BATI is also connected to resistances A2 F2 in preparation for changes in the potential applied to the screen grid electrodes of the channel vacuum tubes Ta Tf. Battery on conductor BATZ completes an obvious circuit to the primary winding (P) Of polarized relay KPI, but this relay remains with its armature engaged to its left contact because the secondary winding (S) of th relay is also energized from battery D connected directly thereto, completing a circuit over its left contact and armature, normally made No. 1 contacts of relays KPZ and KP3, conductors 5 and I2, and the bottom contacts and armatures of relays Re and r Rf to ground. Battery on conductor BATZ is also connected to the windings of relays KPZ and KP3 in preparation for their subsequent operation a described hereinafter.

When the receiving circuit is thus out through to the transmitting station at the beginning of a call, there is a brief period durin which it may be exposed to speech or noise currents which, if the receiving circuit were ready to receive signal frequency impulses, might cause it to operate falsely and thereby cause a false setting of the first settable register ordinarily connected to the front contact of the channel relays. To prevent this, the receiving circuit is normally held in a condition whereby signal impulses cannot be registered until after a definite timed impulse consisting of frequencies 0 and f is received, which impulse is transmitted from the transmitting station by the operation of key KP thereat which, over its left contacts, causes frequency sourc 0 to be applied to conductor SCT and, over its right contacts, causes frequency source 1 to be applied to conductor SCR. These conductors, across which resistance N6 is bridged to supply a matched terminating impedance for the trunk during the time that it is connected to the key-set, join with trunk conductors T and B, respectively and cause circuits to be completed over th left windings of repeating coil BC. The currents of frequency 0 and f flowing over this path causes similar currents to be. induced in the path including the right windings of the repeating coil R0, the trunk conductors T and R, the conductors T and R, the contacts SS1 and SS2 at the sender selector crossbar switch SS, conductors T1 and R1, the front contacts of relay SW, which is assumed to have been operated in any suitable manner, and thence through the pad AP, the filter HPF and the left winding of transformer IT with the grounded: resistances IN bridged thereacross. The signal voltage thereby developed in the left winding of transformer IT is induced into the right winding, amplified through the limiter VL, and then applied, partly across resistance N l and partly across resistance N5, the former being applied to the left Winding of transformer SPT of the signal present circuit and the latter, through resistances N2, N3 and N4, to the input terminals of the channel filters BPF BPFI. Since only the filters BPFc and BPFr are each tuned to pass one ofthe two frequencies in the signal, the voltage thereof is applied to the grid electrodes of vacuum tubes To and. T1 through resistance Cg and Fg but not to any of the other channel tubes.

Now each of the channel tubes Ta Tf (Which are pentode tubes )is provided with a positive grid bias from positiv battery through coil FLT and resistances P4 and P5 and a control grid resistance Ag F9, respectively to make the tube function as a detector. Each channel is also provided, as before stated, with'its own individual relay Ra R), the secondary winding (S) of each of which is connected in the anode circuit of its associated vacuum tube. The primary windings (P) of these channel relays are connected in series and obtain battery through filter coil FLT. The other end of the series connection of the primary windings (P) of relays Ra Rf is connected to resistance CHI and thence to conductor Ll whence it traces back to the upper contact of relay SPR as already shown.

Consequently when the operator depresses key KP before depressing any of the digit keys, a part of the voltage derived from the signal frequencies c and f is applied to transformer SPT to cause the operation of tube S and that of its anode relay SPR which, upon operating, applies ground to conductor J and thence to conductor L and/or L1, resistance CH! and the primary windings (P) of the channel relays Ra Rf, while the remaining voltage is applied (through the respective filters BPFQ and BPFr) to the grid electrodes of tubes To and Ti, respectively. The application of this voltage to the grid electrodes reduces the value of the positive poten tial between grid and cathode normally thereon from battery through coil FLT and network P4 and P5 in consequence of which the respective anode currents flowing through these tubes and the secondary (S), or bias, winding of relays R0 and Ff are reduced, causing these two relays to operate on the current through their operate winding (P), the circuit of which may be traced from battery through the filtercoil FLT, serially through the primary winding (P) of all the relays Ra Rf, resistance CHI and thence as already traced to ground on the contacts of relay SPR. It will be noted that the current which causes the operation of relays Re and R), while flowing through the operate winding (P) of all the channel relays, yet will only cause the operation of the two relays R0 and Rf since the current in the secondary (S) wind- "through in ing of each of the other channel relays has not been diminished by any material alteration inthe control grid potentials of their respective tubes. 1

With relays Re and Rf thus operated, ground is disconnected from conductors 5 and I2, which remove ground from the secondary winding (S) of relay KPI, the path of the ground being by way of the No. 1 normally made continuity contacts of relays KPZ and KP3 and through the armature. and left contact of said relay KPI.

Relay KPI now operates slowly over an obvious circuit through its operate (P) winding, the slowness of its operation being due to the charging current for condenser KPC flowing through its secondary winding (S) and resistance KPRI', which current opposes the current flowing through. the primary (P) winding. When the condenser KPC is completely charged, the current flowing through the winding (S) of the relay is limited by the high resistance KPR, and since the resulting magnetic flux is smaller than that produced bythe current flowing through the primary (P) winding, the relay is caused to operate.

Resistance KPR is provided to insure. that the armatureof relay KPI shall always engage its left contact when the circuit is idle. If.this resistance were omitted, the removal of battery from conductor BATZ during the time between the breaking of the left contact of relay KPI and the operation of relays KPZ and KP3 would leave the circuit blocked since condenser KPC would be charged and no current would be flowing in the secondary winding (S) of relay KPI to release it.

Now when the KP signal is terminated by the release of key KP after the required interval to operate relay KPI, or by any other suitable means such as, for instance, a simple timing circuit responsive to the depression of key KP and adapted. to keep frequencies 0 and f on the trunk conductors for the required interval, the release of either relay R0 or relay Rf will cause ground to be connected to conductors 5 to I2, respectively. Since these two conductors are joined at the No. 1 normally made contacts of relays KP2' and KP3, and since relay KPI is now operated, the ground on conductor 5 or l2 (or both) is applied to the windings of relays KPZ and KP3 via the armature and right contact of relay KPI. Since battery is connected to the other terminals of the windings of each of these two relays by conductor BAT2, both relays will operate and lock to ground on the No. 5 contacts of relay KP2. (The No. 1 front contacts of relays KPZ and KP3 maintain the ground via the armature and contact of relay KPI as relays KPZ and KP3 operate.) Relay KP2, over its No. 8 front contacts, now reapplies ground to the secondary winding (S) of relay KPI, increasing the current flow thereconsequence thereof and causing relay KPI to release and reestablish its armature into engagement with the left contact.

Relays KPZ and KP3, upon operating, perform the general function of extending the upper contacts of the channel relays Ra R1 to conductors A F, five of which, in the register of Fig. 4, extend through contacts on a previously operated steering relay TR! to the lower windings of the relays of the first digit register in which the first operations of the relays Ra R in the proper combinations will be registered. In the register of Fig. 5 an extra vRd,

translating step is required, as explained herein aftenso the six'registering conductors A" IF are connected directly to the windings of six translating relays, the contacts of which are connected through contacts on a previously operated steering relay AC to the lower windings of the relays of the first digit register. With either arrangement, subsequent operations of relay Ra, R) in the proper'combinationf will be registered in the: firstand succeeding groups of register relays. Relays KPZ and K1 3, upon operating, also remove ground from the vacuum tubexside of the resistances A2, A3-F2, F3 but ground is still maintained on each pair of resistanc'e's (as for example, resistances A2, A3) through the lower contact of each channel relay tomaintain the screen-grid electrode of the corresponding channel tube atthe required potential. As. explained in detail later, when the circuit is in this condition the screen grid poten-' tial of each channel tube is changed when the corresponding channel relay operates, whereas in the original condition the operation of the channel relays has no -such effect. In additon, relay KP3, over its No. '7 contacts and conductor I8, supplies ground to the. serially connected tertiary windings (T) of alllthe channel relays Ra Rf. These tertiary windings are poled to oppose the primary'windings (P) of said relays and, for certain operations described: hereinafter, function to release the relays.

As previously. indicated, it is necessary that frequencies c and) be received for a definite-length of time without frequencies a, b, d or eif the circuit is to unlock; that is, if relay KPli to operate and relays KPZ and K1 3 are to operate in consequence of the operation of relay KPH. If an impulse containing one or moreof these latter frequencies should appear at any time beforerelays the corresponding channel relay, or relays, will, of course, operatean'd apply ground to'the secondary winding (S) of "relay KP!- and to con denser KPC via the'No. l and No. 6 back contacts of relay KPZxandKPd, or any of them. This ground. restores the full bias current tothe secondary '(S) winding'of relay KPI, and if this relay. 'had already started to operate (because, say, of thepresence offrequencies c and in the extraneous impulse along with the other frequencies), it will restoreimmediately becauseof the full bias current produced by ground on the secondary winding (S), and condenser KPC will dischargeto said ground inpreparation for a new timing cycle. If relay KPI is normal when the extraneous impulse appears, the application of ground to the secondary winding (S) of relay KP] simply causes the relay to remain. in its unoper'ated position; that is, with its armature engaged with the left contact. In either case, the net result is 1 that the channel relays Rf remain ineffective for the purpose of registering their operated condition until frequencies c and 1 appear by themselves and by themselves only for the necessary length of time, since, with relays KM and KPii'normal, the front contacts of the channel relays are not cutthrough to the register, and the channel relaysthemselves which were operated. by the impulse .will restore when the impulse is terminated since, with the removal of the grid potential from the associated tube by the termination of l the impulse, the full plate current is restoredwhich, flowing through the secondary winding(S) oftheassoxiatedchannelirelay willgcause the latter. to restore It. will KP2 and Klfi' will have been operated,

be noted that during these operations, the screen grid electrode of each tube remains grounded through appropriate contacts of relays KP2 and K1 3 and, therefore, will have no effect upon the intensity of the plate current when the signal potential is removed from the grid. That is, prior to the reception of the KP signal, the channel relays Ra R) are free to operate and release in accordance with the application and removal of the incoming alternating current signals. The reason for this'is because the screen grids of the several channel tubes, being grounded at the contacts of relays KPZ and/or K33, are powerless to change the intensity of the "associated plate currents when the latter increase to their normal strength upon the removal of impulse potential, in consequence of which the several channel relays restore to normal in response to the preponderating bias current flowing through their respective secondary (S) windings. After the IQ signal has been received, however, and relays KPZ; and KP3 have been operated in consequence thereof, the direct ground formerly supplied via some of their back contacts to the screen grid electrodes of all the channel tubes is removed and these electrodes are connected to ground'only as long as their respectiv channel relays remain, on their-back contacts, with the resuit that, when a channel relay operates, the screen grid. potential of .its, associated vacuum tube is changed, in such a way that the relay is locked up. This locking action is caused by the fact that when a channel relay operates, after the anode, current flowing through its bias winding (S) hasbeen reduced sufilciently by the-incoming signal, the operated relay, by causing-its grounded armature to break with its associated back contact, removes ground from the screen grid of its associated vacuum tube and causes-the latter to be connected to a potentiometer which supplies a much lower voltage-than normal between screen grid and cathode, in consequence of which the plate current of the tube-remains reducedafter thesignal has terminated and the controlj grid, electrode has been restored to its normal potential.

Thus-if we assume; that a.- signal made up of frequencies'a. and b is transmitted before the KP -signal 0f;freqllencies-cand f and, therefore, before relays K1 2 and KPS are operated in consequence of, the latter signal, the voltage due to the signal composed of frequencies a and b is appliedto the control grids of channel tubes Ta and Tbyrespectively, and the current through their respective anode; circuits (including the secondary (S) windings of relays Ra and Rb) is reduced, and relays Ra and Rb; operate on the current; flowing. serially through their primary winding. When operated, relay Ra opens one; of the two pathsby which ground-reaches conductor L9,;and relay Rb; opens one ,of: the two: paths by which ground, reaches conductor [4, but, since relays KPZ and K133- are normal, ground is still applied to the screen grid'electrode. of tubes Ta and. Tb via conductors [9.and1ill," respectively, over contacts: Sand 5, ,respeotively,..of relay K23. The presence of: ground on. these electrodeswill causethe reduction of the anode current to be determined exclusively bythe' potential of the signal applied to the control. grids of the respective tubes so that, when thesignalceases, the anode current isrestored toritsor'iginal value and relays Raj and Rbxrele'ase. When, however, a signal. comprising any. two oi the frequencies a I, say frequencies wand c, is: transmitted from the corresponding resistances A2 after the operation of relays K1 2 and KP3 and the consequent removal of ground supplied over their back contacts to leads 6, 8, It, i l, l5 and I9, the corresponding channel relays R0. and Re now operate as before but, in so doing, remove ground from the screen electrodes of their respective tubes Ta and To. With these grounds removed these electrodes are connected to a potentiometer made up of resistances A2 and C2, A3 and the (P) windings of relays CK! (3K3, as follows: Resistances A2 and C2 extending tobattery'over conductor BATE, while resistances A3 and (33 extend to ground via a circuit consisting of the serially connected primary windings (P) of relays CKE, 0K2 and CKEB shunted by the four resistances B3, B3, E3 and F3 in parallel. The potential applied by this network to each of the screen grid electrodes of the tubes Ta and To is lower than that available thereto by the previous ground connection and H this will cause a further reduction in the anode current. When the signal Voltage ceases, the control grids are restored to their normally positively biased state, but since a low potential is still available at the screen grid electrodes from the potentiometer network, the anode current is still reduced in spite of the restoration of the control grid electrodes to their normal state,

thereby causing relays Rd and R0 to remain in an operated condition until their operate (P) windings are opened.

It willbe noted that when relay KPZ operates, it applies ground over its No, 8 contacts to the secondary winding (S) of relay KP! and to condenser KPC in the same way as the channel rerelays are now locked to ground on the No. 5

contacts of relay K1 2. The purpose of this arrangement is to make sure that the timing circuit, comprising relay KPi and condenser KPC, is normal and ready to give a complete timing cycle on the next call, A sequence adjustment of the No. 5 contacts of relay K1 2 insures that these contacts close ahead of the No. 3 front contacts which release relay KPI.

As already stated, the alternating current signal code impulses consist of various combinations of two frequencies a f sent simultaneously according to the code previously given. In the receiving circuit, each frequency finds a path through its corresponding filter to the grid of one of the vacuum tubes Ta To and causes the operation of the associated relays Ra Rf. After the operation of relays KPZ and K1??? by the KP impulse signal which, as above noted, is transmitted ahead of the digital impulse codes, the operation of one or more of relays Ra Rf causes ground to be applied to the corresponding conductors A P which connect with the settable registers or the translating relays associated therewith, causes ground to be removed F2 to reduce the Voltage on the screen grids of the associated vacuum tubes, causes the operated channel relays to lock in consequence thereof as already described and, further, allows current to flow through the primary windings (P) of relays CKLMCKZ and CR3 inan amount almost directly proportional to the number of relays Ra R) which are operated. It will be noted that, prior to the reception of the KP signal, relays CKI, 0K2, 0K3, cannot function because they are, in effect, short-circuited by the grounds supplied to leads E5, 8, it, id, id and it from the back contacts of relays KP2 and KP3.

Relays CKl, (3K2 and CK? are all polarized relays. The operate current through the respective primary windings (P) and the bias currents through the respective secondary windings (S) are so proportioned that none of them will operate When a single channel relay Ra R1 is operated. Relays Clil and CH2 will operate, however, when two of said channel relays operate because of the increase in current through the primary windings (P), and relays 'CKI, 0K2 and (IE3 will operate when three or more of said channel relays operate because of a still higher increase in the current through their respective primary windings (P). Thus, for example, if, after the transmission of the KP signal and, therefore, after the operation and locking of relays KPZ and K1 3, the operator were to depress the digit key l to put forth upon the trunk an impulse consisting of frequencies a and (1, said impulse would cause the operation of relays Ra and Rd, in consequence of which ground would be removed from the screen grid electrodes of channel tubes Ta and Td and, also, from conductors is and it. Now while the current flowing through the secondary windings (S) of relays CKl, 0K2 and (IE3 is fixed and determined by the ohmic resistance of each of said windings and the ohmic resistance of resistors CKl-tl and CKRE, the current that will now flow through the primary windings (P) is determined by the ohmic resistance of said separate windings and by the number of parallel paths to battery BAT2 which will be formed through resistances A2, A3 F2, F3 by the operation of the number of channel relays. In the case assumed, relays Ru, and Ed are operated; consequently, the current through the primary windings (P) of relays CKl, CE? and CK? is determined by resistances A2 and D2, and A3 F3, the actual path tracing from ground, serially through the primary windings (P) of relays CKl, 01222 and C213,,with resistances $.33, C3, E3 and F3 in shunt therewith, resistances and A2 to battery BATI and, in parallel therewith, through resistances D3 and 13?; to battery BATH. The quantity of current flowing through this circuit will produce sufficient magnetic flux in the relays to overcome the flux due to the current flowing through the secondary windings (S) of relays CKi and (3K2 and will cause said relays to operate, but this current will not produce sufficient flux to overcome the current through the secondary winding (S) of relay (3K3 which, on this account, remains unaffected. Relays CKE and C52 will remain operated until ground is reapplied to conductors i 53 and it on the release of relays Ra and Rd, which will be described later.

Should there be three frequencies in a digital impulse, say frequencies a, d and c, then relay To will operate along with relays Ta and Td, and ground will be removed from one side of resistances C2, C3 whereupon the circuit of reiays 0K1, (IE2 and CH3 will take on an additional parallel branch through resistances C2, 63 to battery BATH, resistance C3 being removed as a shunt around relays CK! 0K3, and the current flowing through the primary windings (P) of relays Clii, (3K2 and (IE3 will beinnels.

creased so that, this time, the flux will be sufficient to overcome the flux due to the current flowing through the secondary winding (S) of relay (3K3, which will now operate alongwith relays CKI and 0K2. Relays CKl, GK? and 0K3, therefore, serve to check each of the incoming signals and, as will be shown, will advise the sender whether or not it should register these signals.

Considering the. operation of the receiver in connection with the settable registers of Fig. 5, (and Y wiring in Fig. 3) the operation of relay CKZ removes ground from conductor M and applies it to conductor J in parallel with the ground applied to this conductor by relay SPR. Relay CKI, when operated, removes a short circuit around resistance CH2 and eifectively adds this resistance in series with the primary windings (P) of the channel relays Ra, Rf, by insorting this resistance between conductor LI and conductor L, the latter joining conductor J at the contacts of relay PT. With theprimary windings (P) of relays Ra. Rf connected through resistance CHI to ground, the circuit hasits full sensitivity, but after relay CKil operates and resistance CH2 is inserted in series with resistance CHI, the sensitivity is somewhat reduced. The reason for this slight decrease in sensitivity is to increase the protection against false operations on transients and cross-modulation which may appear in the unwanted chan- Relay CKl also applies ground from relays SPR and/or CKZ via conductors J and L, as traced above, to conductor H, in consequence of. which a circuit is completed for relay TG over its No. 2 normally made continuity contacts, causing said relay to operate and look over its No. 2' front contacts to ground on conductor J. Relay TG performs a function which willbe shortly described.

As previously indicated, the path betweenconductor J and conductor L is closed in the sender at the start of each digit and remains closed until the sender opens it, after the registration of each digit, by the operation of relay PT, as hereinafter described, whereupon the channel relays are released by virtue of the fact that the'circuit of the primary windings (P) of the channel relays is-opened at the contacts of relay PT. Once this has occurred, the path to the primary windings (P) of the channel relays remains open and the channel relays remain re leased until relays SPR and CK! both release and. remove ground from conductor J, since, until this occurs, relay TG remains locked to prevent the release of relay PT; It will be noted, however, that, although the path to the primary windings (P) is opened at the contacts of relay PT,. the operation of relay KPE' has applied ground over its No. '7 contacts to conductor l8 which is connected serially to the tertiary winding (T) of the channel relays, the circuit thereof being completed to battery through retard coil FBI. Now the tertiary winding (T) of each channel relay is connected so that the current flowing through it as a result of the circuit closed by the operation of relay K1 3, is in a direction to release the relay; that is, the current is in a direction to aid the'bias or secondary (S) winding and to oppose the current flowing through theprimary (P) winding; Consequently, when the primary circuit is opened at the contacts of relay PT, the operated channel relays will release, either in consequence of the current fiowing' through their respective tertiary windings (T)-if the signal impulse'is not terminated, or in consequence of the resultant effect of the current flowing through their respective tertiary windings (T) and the current flowing through their respective secondary windings (S) if the signal impulse is terminated. Although current will, of course, flow through the tertiary windings (T) of the channel relays when current is also flowing through their primary windings (P), the combined effect of the reduced current in the secondary winding (S) of the relays affected by a signal frequency and the current flowing through their respective tertiary windings (T), will not be sufiicient to overcome the current flowing through their respective primary windings (P), in consequence of which said relays will operate and remain operated until the primary circuit is opened at the contacts of relay PT. Those channel relays which do not have a signal voltage applied to the grid of their asso ciated' channel tube will have full current flowing through their respective secondary windings (S) so that these relays will remain in a released condition. Prior to the operation of relay PT as described hereinafter, the ground applied to conductor J over the upper contacts of relay 0K2 insures that the digit will be registered correctly on short pulses. The reason for this is the fact that relay CKZ is held up by the looking circuit of relays Ra. R as previously described, while the ground through the upper contacts of relay SPR. insures that there is no double registration in case. the incoming signal persists for a longer time than actually required for registration; that is, for a longer time than it takes relay PT to operate.

The registration in the sender of the succession of signal impulses transmitted from the transmitting station by the depression thereat of the appropriate sequence of digit keys of'the key-set KS subsequent to the depression ofkey KP, depends upon the construction of the sender, the

character of the settable registers therein and the manner in which these registers are to be set in response to the operation of the register relays in the combination of twos required by the frequency pulse code. Fig. 5 schematically shows the portion of a sender which, for instance, may be located in ofiice X for the completion of a connection to a local station C, or to a telephone station E, the latter being locatedin ofic'e Y. If these stations are also to be reached from a call originating in oifice X through an operator's position provided with facilities'for keying a series of direct current pulses representative of the called station designation, then the sender must be provided with corresponding facilities to register alternating current pulses whenthe call originates from an alternating current key-pulsing station and to register direct current impulses when the call originates at a direct current keypulsing station. The register for a'sender adapted to handle both types of calls is'illustrated in Fig. 5 and will be considered hereinafter. Fig. 4, on the other hand, shows schematically the portion of a sender which, for instance, might be used at oiiice X for completing calls to a subscriber in that office only, such as subscriber C, when it is not necessary to accept calls from operators equipped with direct current key-sets or to complete calls to other ofiices, such as ofliceY. One of the characteristics of this register circuit, as compared with'that of Fig. 5, is that it must always be supplied with a'full complement ofdigit signals and that, having received them, it tells the'senderto proceed with the call withoutwaitcase, which will be apparent from the more complete descriptions of the two arrangements that follow.

Considering first the registers of Fig. 4 (X wiring in Fig. 3) andassuming the same to be incorporated in a sender adapted to register only alternating current impulses of the character described (in which event relay SW will not be provided and conductors TI, RI will be connected directly to the inputterminals of pad AP), the seizure of the sender at the sender selector switch SS and the connection of the sender with the trunk will initiate circuit operations among which are, as said before, the connection of battery to conductors BATI and BATZ, and the operation of the steering relays TRl and TRA by the application of momentary ground to conductor 2B, whereupon both relays lock serially to ground on the left contacts of relay TRA while relay TRI is furnished with a supplementary holding path over its No. 6 front contacts and conductor H to ground on the upper contacts of relay CKI when the latter operates on the regular digit pulse. At the same time, the other pairs of steering relays, TRB and TRZ, TRC and TR3, etc., up to the final pair 'IRN and CI, of which only relays TRB, 'IRZ, TRN and CI are shown for the second and succeeding registers are operated, one from the other in succession until all'of them are operated and locked up. With the operation of relay TRI, the five signaling conductors A E (conductor F has a different connection in a settable register of the kind shown in Fig. 4) are connected, respectively, to the operating windings of the five relays l 5 constituting the register for the first digit and, after relays KPZ and KP3 have been operated by a KP signal, obvious circuits are completed from ground on the upper contacts of the channel relays Ra Re operated in combinations of two according to the code given, over the appropriate two of the five conductors A E, two armatures and right front contacts of relay 'IRl to the lower windings of the two corresponding relays of the five register relays I 5 of the first digit register. tered and relay CKI is released, relay TRI is released and the signaling conductors A E are advanced over back contacts of relay TR] and front contacts of relay TRZ to the operating windings of the relays l 5 of the second digit register. relays in the first digit register are locked up to ground on the No. "I normally made contacts of relay 'I'Rl, and conductor H is extended to relays TRZ and THE. Similarly, when the second digit is registered and relay CK! is released, relay TR2 releases and the five signaling conductors A E and conductor H are extended to the third group of steering and register relays, and

so on until the last digit is registered, whereupon relay CI releases and opens conductor L to stop the reception of any further digit indications, thus reventing the reception of the ST signal, as previously indicated. If this signal should appear before the last digit is registered, how- When the first digit is regis At the same time, the operated contacts No.2 of relay CI.

ever, it will cause the application of ground to conductors E and F, and since conductor F is connected to the reorder circuit, further registration will be stopped and a reorder signal will be sent back to the transmitting station as an indication of an error which must be corrected by retransmitting the whole number.

With this register arrangement, the registration of eachdigit is indicated by the operation of two relays in a particular register and it is possible to give a definite indication that the reg istration is completed, which may be accomplished by means of polarized marginal relay TO' which operates over its primary winding (P) as soon as two register relays of the connected register close their locking circuits, as shown hereinafter, but which will not operate when only one relay of said register operates.

Thus when a digit signal comes in, say the signal of digit 9,'the pulse code of which is frequencies at and e, relay SPR operates to supply operating ground to the operate windings (P) of the channel relays Ra Rf. Relays Ra and Re operate and lock in response to the frequencies in the signal, and relays'CKl and'CKZ also operate for the reasons already given. 'Ground applied to conductor Hfby relay CKI short-circuits relay TRA which releases and thereby removes the ground it was supplying to the winding of relay TR I, but the latter remains locked to ground on conductor, H over its No. 6 front contacts until relay CK! releases. Circuits are now closed for register relays l and 5 of the first digit, register, the circuit of the former being traced from ground on theupper contacts of re-' lay Ra, conductor 2l, No.6 front contacts of relay KP3, conductor A, No.1, front contacts of relay 'I'Ri," lower winding of relay i to battery; the circuit of relay 5 being traced from ground on the upper contacts of relay Re, conductor 1, No. 4 front contacts of relayflKPZ, conductor E, No. 5 front contacts of relay 'IRl, lower winding of relay 5 to battery. Relays l and 5, upon operating,'close a path from battery through their respective upper windings and locking contacts,

No. '7 front contacts of relay TRI, right contact-s i of relay TRA, winding (P) of relay TO, contacts of relay CKA, conductor K, lower contacts of relay CKS, which is normal since only two frequencies are present in the signal, to ground. Relay TO operates, disconnects the resistance ground being supplied over conductor J from resistance CH2 via the front contacts of relay SPR and/or relay 0K2, to the operate winding (P) of the channel relays, and locksitself to saidground on conductor J via its armature and front contacts, secondary: windings (S) i to battery via (Since both the (P) and the (S) windings of relay TO cause said relay to operate, a biasing spring or other suitable means must beprovided to release it.); If the signal is short and relay SPR releases before registration is completed, relays Ra and Re are, nevertheless, held operated by the ground sup plied to conductor J through resistance CH2 and the upper contact of relay (2K2 until" relay TO operates to signify thatthe registration of the digit has taken place. If the signal remains on longer than the time required for the register relays and relay TO to operate, the channel relays Rd and Re release but relay, TO, which has been locked up as previously described, remains operated untilgrelay SPR releases at the end of the signal pulse. V

Whenthe channel relays Ba and Re release,

relays CKI and CK2 release also, the former disconnecting ground from conductor H to cause the release of relay 'I'Rl which, in consequence, ad vances the signaling conductors A E over its No. 1 .5 back contacts, respectively, to the ar matures of the No. l 5 contacts, respectively, of thenext transfer relay TRZ from which they are extended via the front contacts of that relay to the register relays of thesecond digit register. The release of relay TR also advances conductor H over its No. 6 back contacts and the No. 6 front contactsof relay TR2 to the winding of that relay and that of relay TRB, and, in addition, relay 'IRl, at its No. 7 contacts, opens the connection from the winding (P) of relay TO to the first digit register and provides a ground for locking the two operated register relays l and 5 ,in that register; The register circuit is 'now ready for the second digit signal, after the re oeption of which it advances to the third digit H register and so on until all of the digits have been registered. When ground is removed from conductor H at the end of the final digit signal, relay CI is released, and since it opens lead L at its No.l contacts and therefore, lead Ll, further operation of, relays Ra. R in the receiving circuit is prevented. Relay Ci, through its No. 2 contacts, also opens the locking battery for relay TO and by means of contacts not shown causes the sender to advance the call.

should only one channel relay operate due to i the presence of one frequency in the impulse produced, say, by some abnormal condition, the corresponding register relay would operate also, but the latter would not lock up since, with relay CKI released, no ground'would be applied to conductor H and relay TBA would not release in consequence thereof and no locking circuit for the register relay would be available through. the primary winding (P) of relay TO. Should more than two channel relays operate, then relay (3K3 would operate in addition to relays GKl andCKiZ for the reason already 'advanced and relay 0K3, upon operating, would 'apply'ground to conductor R0, completing thereby a circuit to a suitable freorder. circuit which would function to cause the reorder signal to be sent back to the transmitting station, the meaning of which, to the operator th'ereat, would be to retransmit the en- 'tire number. Relay CK3, by breaking its lower contact, disconnects ground from conductor K to prevent relay TO from operating. t

' Relay CKA, whichis of the slow-releasety-pe, is normally operated by ground on conductor M applied thereto throughthe back contacts 'of relay CKE; It is released when relay CKZ operates, and serves to delay the closing of'the regist'er locking circuit and hence the operation of relay T0, for a short interval in order to allow ample time for relay (3K3 to function in case one or more interfering frequencies should cause theoper'ation of more than the two channel relays which would be operated by a normal digit JimpuIsei Fig.5 schematicallyshows the registering ele- .ments of a sender in which each of the digit reg =isters comprises four relays instead of five. slender of this type is available not only to the trunked connection from the distant transmitting station where alternating current keying is used, butalso to a local operator at ofiice X whose position is equipped 'for direct current keying of impulses by which to obtain the number of the called station as, for instance, the

position typified by the-cord GDequipped with ent set of registers must be provided for each code or'one set of registers for both and a translating arrangement by which one code is changed into the other. For practical reasons the latter, or translating arrangement, is shown; and since the direct current pulse code is the basic one, the alternating current signal indications are converted into equivalent direct current pulse indications, the digit registers taking the direct current pulse code setting for the same digit whether the digit is transmitted by direct current pulses from the key-set DA or by alterhating current pulses from the key-set KS.

The translator comprises the six relays TA TF shown in the lower part of Fig. 5 but only a portion of their respective contact equipment and interconnecting wiring is shown.

The six translator relays TA 'IF are o'per ated by the channel relays Ra Rf over con-'- ductors A F, respectively, when the latter relays operate after the KP signal has been received and relays KP2 and K1 3 have been op erated in consequence thereof, relay TA being operated by relay Ra, relay TB by relay Rb and so on up to and including relay TF which is operated by relay Rf.

In order to simplify the understanding of the operation of the translator, the table below is furnished to show, for each digit, what combination of translator relays is operated in accordall) til

current key-pulsing circuit DCP.

Digit Leads grounded r direct current operation Digit TM, RP

It will thus be seen from the above table that, with the four-relay digit register, the numberof relays operated to indicate the different digits yaries from none for the digit0 'to three for the digit 3 when relays l, 2 and 5 are op erate'd. If the relays are given appropriate numerical designations, this system has the advantage that the digit itself may be identified by adding up the'designat'ions of the operated register relays. It lacks, however, the positive indication that the registration of a digit has been completed, which is obtained with the fiverelay digit register pr Fig. 4 wherein two relays,

and only two, are always operated iper digit and tion." As a consequence, it, is not possible to use a marginal relay TO, as in the register of Fig. 4, to indicate that the register is satisfied, but a timing circuit must be used to insure that the channel relay circuits to the several register relays are maintained long enough for the slowest relay of the register to operate. The timing interval is obtained from polarized relay PT which is made slow-operate by means of the condenser PTC and resistance PTR associated with the right winding (R)v of the relay, to the joint terminal of both windings of which battery is connected, through the left contacts of relay ACP, which, along with relay ON, is operated in any suitable manner when the sender is seized for use on calls using alternating current key'pulsing. .As long as ground is supplied to the right winding (R) over conductor M via the No. 1 contacts of relay TG from the lower contacts of relay CK2, relay PT isheld in the releasedposition by the current flowing through saidv right winding (R), during which time condenser PTC is, of course, short-circuited. But when ground is removed from conductor M by the operation of relay CKZ, a charging circuit for condenser PTC is established from ground through resistance PTR, condenser PTC, right winding (R) of relay PT to battery on the left contacts of relay ACP. The charging current of the condenser is in the same direction as the current produced by the circuit completed by ground on conductor M so that, during the time that the flux produced by the charging current predominates over that of the current flowing through the left or operate winding of the relay, the armature of said relay remains engaged to its contact to maintain ground to the operate windings of the channel relays via conductor Ll, resistance CH2, conductor L, contacts of relay PT, conductor J to ground on the upper contacts of relay SPR and/or the upper contacts of relay CKZ; When, however, the resulting flux drops below that due to the current flowing through the left winding (0) of relay PT, said relay operates and disconnects ground from the operate winding (P) of the channel relays with consequences already noted in connection with the register shown in Fig. 4.

The relays I, 2, 4 and 5 of the individual digit registers are operated by grounds on conductors TM, TP, RP and RM, respectively, while the steering relays AC and AL, corresponding, respectively, to the relays TRI and TRA of the register of Fig. 4, are controlled by ground on conductor TS. Relays AL and AC are operated in series by momentary ground on conductor and locked up to ground over the left contacts of relay AL, and at the same time the other pairs of steering relays (not shown) between AL and AC and the steering relays NL and NC for the final register are operated, one from the other in succession, until they are all operated and locked up. With relay AC operated th conductor TM, TP,RP and RM are connected to the operate windings of the relays in the first digit register.

When direct current pulsing is involved as, for instance, in establishing a call from a subscriber in ofiice X via a local position thereat to another subscriber either in the same oince or another oflice, in such cases the sender is connected to the local trunk terminating in jack LJ in response to the operator having seized said trunkby plugging cord CD therein. Cord CD- has the usual facilities for connecting thekeyset DA across the tip and ring of the trunk, for initiating the operation of circuits by which the selected sender is connected to the trunk LJ via,

the crosspoints LSSI and LSS2 at the sender selector switch SS through conductors TTand RR. Since, in this case, relay SW is normal, the trunk conductors, instead of being connected to the alternating current pulse receiver are connected to a direct current key-pulsing circuit DCP which responds to the key pulses and, in response to the operation of each digit key, causes ground to be applied to conductors TM, TP, RP and RM in accordance with the digit keyed. The grounds on these leads then complete circuits to relays I, Z, 4, and 5 of one of the digit registers (which one depending upon the number of pairs of steering relays which have been released as the call has progressed) causing the operation of said relays in accordance with the code given, said relays looking over their upper windings and contacts to ground on relay ON which is operated at this time. Since this partof the sender equipment and its operation form no part of this invention, no further description of its operation is considered necessary.

As before indicated, relays. TA TF oper ateon the two-at-a-time basis in accordance with the alternating current pulse code, and the connections through their contacts are such that each pair that corresponds to a digit code will set up a path to the proper conductors TM, TP, RM and RP. For simplicity, only the path for the translation and registration of the digit 1 in the first digit register is shown, concerning which, when relays TA and TD operate in response to the alternating current signal pulse of the digit 1, a circuitis completed for relay i of the first digit register, extending from battery through the lower winding of said'relay, No. 1 front contacts of relay AC, conductor TM, No.15 contacts of relay TD, No. 4 contacts of relay TA, to ground. Digit relay I operates over its lower winding and then locks overits upper winding and up-. per contacts to off-normal ground on relay ON.-

Relays TA 'I'F, when operated in groups of twos according to the alternating current impulse code above given also connect ground to the steering conductor TS,.the path being traced from the right contacts of relay ACP, through a set of operated contacts on each of the two operated relays and. a set of normal contacts on the unoperated relays of the translator. Ground on conductor TS short-circuits relay AL, which releases, but it holds relay AC operated until the tWo operated relays of the translator release in response to the release of their associated chan- .nel relays, at which time relay AC will release station under these circumstances, since the com-.

bination of frequency ,f with any other frequency except 6 (after the KP signal) is not an as- I signed code, and the reception of such a signal is therefore an error, which can be rectified only by retransmitting the whole number. The combination of relays TE and TF is th code of the start signal which is accepted in the same way as the digit signals. It is transmitted from the transmitting station by the depression of key ST thereat after all th digits are sent and, in the consequent operation of relays TE and TE, circuits are completed through th contacts'of saidrelays to operate digit register relays i and 4,'which in turn provide a signal for the sender to proceed with the setting up of the connection.

' The circuit is made inoperative to the operation of. a single translator relay by arranging theconnections in such a manner that two translator relays must be operated in order to apply ground to conductors TS, TP, TM, RP and and alsoby. preventing the operation of relay PT, which. i held released by ground supplied to its right winding (B) through normal contacts on relay 0K2 and relay TG, neither of which will operate unless two channels have been energized (relay TG being under the control of.

relay CKi, which also requires that two chan- TA TE operate as previously described and,

when two relays are up, close ground to the proper conductors TP, TM, TS, RP and RM of the digit register reIayscausing the release of relay AL and the operation of the required relay, or

relays, in the first digit register while holding relay AC operated. At the same time, relay TG operates over the following path: ground through the make contacts of relay SPR and/or relay M 0K2, conductor'J, normal contacts of relay PT, conductor L, make contacts ofrelay CKI, conductor H, N o. 2 normally made contacts and winding of relay TG to battery. When operated, relay TG looks through its No. 2 front contacts to ground on conductor J from relay SPR and/or 0K2, and through its No. 1 contacts opens the. path between the winding (R) of relay PT and conductor M, from which ground has already been removed by the operation of relay (3K2. Remov ing ground from conductor M starts the timing cycle for the operation of relay PT which, operating after condenser PTC is chargedbreaks the connection between conductors J and L. If relay SP has already released, the two channel relays in the group of relays Ra Rf which were operated by the incoming signal release and cause the release of all other above-mentioned relays except the register relays locked to ground. on the contacts of relay ON. If relay SP is held up by a long incoming signal, all of the relays release except relays TG and PT, which wait until relay SP releases, due to the locking of relay TG to conductor J as described above. When relay AC releases, following the removal. of ground from conductor TS, conductors TM, TP, RM,..RP, and TS are transferred from the first digit register and steering relays to the second, and when the second and the succeeding digits are received the registration continues in a similar manner until the incoming start signal transmitted from the transmitting station by the depression of key ST thereat indicatesv that the last digit has been transmitted. The ST signal operates translator relays TE and TF, in turn operating relaysl and 4 of a register succeeding the register which has taken the registration of the last digit transmitted (the number of digits which may be transmitted may vary depending upon th route and the called oflice) and a circuit closed through a pair of operated contacts on relays i to 4 of any register will operate a start circuit (not shown) which advises the sender. that no more digits will be forthcoming and that, therefore, it may-proceed with the necessary steps to complete the connection. 7

With eithertype of register sender, the registration of the required number. of digits therein indicative of. the route of the call (as, for example, thefname or number of the terminating exchange and/or the called number), causes the sender to become connected to a control circuit known as a marker. in which, over contacts not shown on the digit registers, the necessary digits registration is transferred therein. In response to this registration, the marker then operates over certain control circuits to cause the selected trunk to become connected with another trunk to the terminating office or to the called line, whereupon the marker then disconnects. and the sender proceeds to complete the connection at the terminating office or'drops off if its work has been completed. Since these operations form no part of our invention, the same being well-known marker operations, they are not described here- While we have described our invention in connection with its specific application to two representative types of register senders for establishing automatic telephone connections, it is to be understood that. various other applications and embodiments thereof may be made by those skilled in the art withoutdeparting from the spirit of the invention as defined within the scop of the appended claims.

Whatis claimedis:

1. In a signaling system in combina ion, a transmission line, means for transmitting current'impulses of voice frequency over said line, a signal receiver, ,and means associated with said receiver and-responsive thereto when operating in response to an impulse of predetermined duration for changing the condition of said receiver from a nonrlocking to a locking condition.

2. In a signaling system in combination, a transmission line, means for transmitting current impulsesiof voice frequency over said line, a signal receiver, a register, and means, associated with said receiver and responsive thereto when operating in response to an impulse of predetermined durationfor locking said receiver under the control of said register for each succeeding impulse. 4

3. In a signaling system in combination, a transmission line, means for transmitting current impulses of voice frequency over said line, a signal receiver comprising a detecting device for each frequency, means associated with said receiver and responsive thereto-when operating in response to an impulse of predetermined duration for changing the electrical condition of each ofsaid detecting devices whereby said devices operate in response to their respective frequencies prior to said impulse of predetermined duration and operate and locks in response to their respective frequencies subsequent to said impulse of predetermined duration.

4. In a signaling system in combination, a transmission line, means for transmitting current impulses of voice frequency over said line, a signal receiver comprising a detecting device for each frequency, a register, means associated with said receiver and responsive thereto when operating in response to an impulse of predetermined duration for placingsaid detecting devices under the control of said register whereby said devices op eratein response to their respective signaling frequencies prior to said impulse of predetermined duration and lock under the control of said register subsequent to said impulse of predetermined duration.

5. In a signaling system in combination, a transmission line, means for transmitting current impulses of voice frequency over said line, a signal receiver comprising an electronic device for each signaling frequency, each of said electronic devices having two control electrodes, means associated with said receiver and responsive thereto when operating in response to an impulse of predetermined duration for changing the electrical condition of each one of said electronic devices whereby prior to said impulse of predetermined duration each device operates in response toa potential derived from the signal frequency applied to one of its respective two control electrodes and subsequent to said impulse of predetermined duration it locks in response to a potential applied to the other of its two electrodes.

6. In a signaling system in combination, a transmission line, means for transmitting current impulses of voice frequency over said line, a signal receiver comprising an electronic device for each signaling frequency, each of said electronic devices having two control electrodes, a register, means associated with said receiver and responsive thereto when operating inresponse to an impulse of predetermined duration for changing the condition of said electronic devices whereby prior to said impulse of predetermined duration each device operates in response to a potential derived from a signal frequency applied to one of its respective two control electrodes and subsequent to said impulse of predetermined duration it looks in response to a joint control exercised by a potential applied to the other of its respective two control electrodes by said means responsive to said impulse of predetermined duration and by said register.

7. In a signaling system in combination, a transmission line, means for transmitting current impulses of voice frequency over said line, a signal receiver, means associated with said receiver and responsive thereto. when operating in response to a signal of predetermined duration for changing said receiver from a condition of response to current impulses to a condition of response and locking in response to said current impulses, a register operatively responsive to the locked condition of said receiver, and means under the control of said register for unlocking said receiver and .for reestablishing said firstmentioned means for response to said receiver when operating on a current impulse of predetermined duration.

8. A signaling system comprising a transmission line, a plurality of voice frequency current sources, means for keying said voice frequency current sources over said transmission line in combination according to a code, a receiving system associated with said transmission line comprising a filter individual to each frequency adjusted to permit the passage of the current frequencies incoming over said transmission line, a vacuum tube rectifier individual to each filter having its input circuit connected to said filter for response to a potential derived from its frequency, a relay in the output circuit of each of said vacuum tube rectifiers, a control electrode in each of said vacuum tube rectifiers, and means for applying a potential to said electrode for controlling the current through the output circuit after the signal potential has been removed from the input circuit.

9. A signaling system comprising a telephone channel adapted to transmit voice frequency currents, means for impressing upon said channel current impulses composed of trains of oscillations of different voice frequency components combined according to a predetermined code, means connected to said channel for segregating and rectifying each component, a register, and means responsive to an impulse of predetermined duration for operatively associating said telephone channel with said register whereby succeeding impulses are registered therein.

10. In a signaling system, a transmission line, areceiver connected to said line adapted to receive plural frequency signals within the voice range, a filter individual to each frequency adjusted to permit the passage of the current frequencies incoming over said transmission line,

an electronic device individual to each filter having a permanently activated cathode-anode circuit and control elements of which one element is connected to the associated filter, a relay individual to each electronic device having a first winding in the anode circuit thereof andanother winding, another electronic device operative in response to one or more signal frequencies for completing a circuit through said other winding of each of said relays whereby the effect of the currents through both windings is substantially canceled, whereby the concurrent application of v a signal potential to one of the control elements of one of said electronic devices causes current to be reduced through its anode circuit and including said first winding of the relay included in said circuit, and whereby said relay operates in consequence of the net effect of the current flowing through its other winding and the reduced current flowing through its first winding, and a source of controllable potential applicable to said other control element of each of said electronic devices for holding the anode current flowing through the first winding of their respectively associated relays in a reduced state after signalpotential has been withdrawn from said first control element of each of said electronic devices.

11. In a signaling system, a receiver therefor adaptedfor the registration of plural frequencies, impulses transmitted over the system comprising a channel for each signal frequency, each of said channels including a relay adapted for operative response to the application to the channel of a signl potential derived from a signal frequency, means for locking said relays when operated, and a circuit for rendering said means eifective comprising a polarized relay responsive to the operation of a particular combination of frequencies for a predetermined duration, and a plurality of relays operative upon the release of said polarized relay subsequent to the release of said combination of channels when their respective signal frequencies are withdrawn.

12. In a signaling system, a receiver therefor adapted for response to two-frequency signals transmitted over the system which includes a signal receiving channel for each frequency, and a circuit for checking the number of frequencies in a signal, said circuit comprising three relays and a potentiometer network one branch of which includes a winding of each of said relays serially connected, the intensity of the current flowing through said branch of said potentiometer being controlled by the number of signal receiving channels operated, zero current flowing through said relays from said potentiometer prevailing when no channels are operated and the maximum current to cause all of said relays to operate prevailing When three or more signal receiving channels are operated.

13'. In a signaling system in combination. a transmission line, means for transmitting alternating current impulses over said line, a signal receiver responsive to said impulses, and means associated with said receiver for prolonging the response of said receiver beyond the period of said impulses.

14. In a signaling system in combination, a transmission line, means for transmitting alterhating current impulses over said line, a signal receiver responsive to said impulses, and means associated with said receiver and responsive to said impulses: for prolonging the response of said receiver beyond the period of said impulses.

15. Ina signaling system in combination, a transmission line, means for transmitting altermating current impulses of one or more froquencies over said line, a signal receiver responsi ve to saidimpulses, and means associated with said receiver and responsive to said impulses for prolonging. the response of said receiver if said impulses comprise two or more frequencies,

16. In asignaling system in combination, a transmission line, means for transmitting alternating current impulses of varyingduration over said' li ne, a signal receiver responsive to said impulses, a register responsive to saidreceiver and settabie accordance with the operation thereof to record said impulses; and means for prolon ging the response of said receiver for a time beyond the period of short duration impulses which is just suilicient to fully record the said short duration impulses in said register.

7'. In a signaling system in combination, a transmission line; means for transmitting alternating current impulses over said line, a signal receiver responsive to said impulses, and meansfor reducingthe sensitivity of said receiver after two signaling frequencies have been received.

rs. In a signaling system incombination, a transmission line, means for transmitting alternating current impulses over said line, a signal receiver responsive to said' impulses, a register responsive to said receiver and settable in acco-r'ci'a-nce with the operation thereof to recordsa-id impulses; means for reducing the sensitivity of saidrecei'ver after an impulse comprising two signal frequencies has been received, and means for holding said sensitivity reduced until said impulses are recorded in said register.

l*9=. In a signaling system in combination, a

transmission line, means for transmitting alternating current impulses over said line, a signal receiver responsive to saidimpulses, a plurality of registers, means for connecting one of said registers to said receiver and settable in accordance with the operation thereof to record an impulse, and means for connecting said receiver to a succeeding register in preparation for recording a succeeding impulse regardless oflthe persistence or termination of the preceding pulse in said receiver. 7

20. In a signaling system in combination, a transmission line, means for transmitting alternating current impulses over said line, a signal receiver responsive to saidimpulses, a plurality of registers,-means for connecting one of said registers to said receiver and settable in accordance with the operation thereof to record an impulse, means for advancing said receiver into connection with a succeeding register in preparation for recording a succeeding impulse therein, and means for preventing said succeeding register from recording a prolongation of the impulse recorded in the preceding register.

21. In a signaling system in combination, a transmission line, means for transmitting alternating current signal impulses over said line, said signal impulses comprising pairs of, free quencies in accordance" with. a'prearranged' code, a signal receiver responsive to: said signal impulses, and means associated'with said receiver for giving an indication when the received. signal impulses consist of. frequency combinations other: than those or the prearranged code.

22.. In a signaling system in combination, a transmission line, means for transmitting alterhating current; signal impulses over said line, a signal receiver responsive to said signal impulses, a register responsive to: said receiver and settahle inv accordance with the operation thereof to: record the received impulses,- and. means associatedfwith said. receiver for giving an indication when said signal impulses are received at a rate too fast for said register to records them.

23 signaling system in combination; a transmission line, means for transmitting alternating current signal impulses over said line, a signal receiver responsive to said signaliimpulses, a register" responsive to said receiver and settable" in accordance with the operation thereof to record received impulses,v and means associated with said receiver'for giving an-indicatiorr when said impulses are received with insufficient time interval between them for said register to record them.

GEORGE HEIGHT. ALEXIS A. LUNDSTROM. EDMUND R; TAYLOR, 

